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A hybrid excitation multi-degree-of-freedom spherical motor (HE-MDOFSM) is designed, which can achieve MDOF motion by cooperatively controlling the excitation current in 12 sets of stator windings. The designed motor has the advantages of high power density and a large motion range. In addition, because the designed motor has an irregular three-dimensional (3D) structure, it is difficult to perform dynamic magnetic field calculations with existing methods. To solve this problem, we propose a modified 3D dynamic magnetic equivalent circuit (3DD-MEC). The proposed method establishes a node network according to the structural edge features of the motor core and the permanent magnet and calculates the reluctance of the connecting branch based on the differential principle. Moreover, a connection strategy of air-gap nodes in 3D space is formulated, and the magnetic saturation characteristics of the iron core are reflected by an iterative calculation of magnetic permeability. Using the 3DD-MEC method, the 3D dynamic magnetic field information of the HE-MDOFSM can be quickly and accurately calculated. Finally, the reliability of the method is verified by simulation and experiment, which provides a reference for improving the design optimization efficiency of HE-MDOFSM. [ABSTRACT FROM AUTHOR]